全文获取类型
收费全文 | 5477篇 |
免费 | 164篇 |
国内免费 | 951篇 |
专业分类
化学 | 2824篇 |
晶体学 | 2篇 |
力学 | 389篇 |
综合类 | 190篇 |
数学 | 1069篇 |
物理学 | 2118篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 16篇 |
2015年 | 29篇 |
2014年 | 15篇 |
2013年 | 59篇 |
2012年 | 74篇 |
2011年 | 974篇 |
2010年 | 510篇 |
2009年 | 548篇 |
2008年 | 80篇 |
2007年 | 91篇 |
2006年 | 141篇 |
2005年 | 316篇 |
2004年 | 939篇 |
2003年 | 555篇 |
2002年 | 434篇 |
2001年 | 329篇 |
2000年 | 106篇 |
1999年 | 103篇 |
1998年 | 135篇 |
1997年 | 91篇 |
1996年 | 78篇 |
1995年 | 47篇 |
1994年 | 54篇 |
1993年 | 196篇 |
1992年 | 164篇 |
1991年 | 106篇 |
1990年 | 98篇 |
1989年 | 97篇 |
1988年 | 83篇 |
1987年 | 6篇 |
1986年 | 61篇 |
1985年 | 8篇 |
1984年 | 20篇 |
1983年 | 2篇 |
1979年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有6592条查询结果,搜索用时 31 毫秒
1.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
2.
Peng Zhao Juping Yang Yuming Shang Li Wang Mou Fang Jianlong Wang Xiangming He 《天然气化学杂志》2015,(2):138-144
Surface chemical modification of polyolefin separators for lithium ion batteries is attempted to reduce the thermal shrinkage, which is important for the battery energy density. In this study, we grafted organic/inorganic hybrid crosslinked networks on the separators, simply by grafting polymerization and condensation reaction. The considerable silicon-oxygen crosslinked heat-resistance networks are responsible for the reduced thermal shrinkage. The strong chemical bonds between networks and separators promise enough mechanical support even at high temperature. The shrinkage at 150 C for 30 min in the mechanical direction was 38.6% and 4.6% for the pristine and present graft-modified separators, respectively. Meanwhile, the grafting organic-inorganic hybrid crosslink networks mainly occupied part of void in the internal pores of the separators, so the thicknesses of the graft-modified separators were similar with the pristine one. The half cells prepared with the modified separators exhibited almost identical electrochemical properties to those with the commercial separators, thus proving that, in order to enhance the thermal stability of lithium ion battery, this kind of grafting-modified separators may be a better alternative to conventional silica nanoparticle layers-coated polyolefin separators. 相似文献
3.
Zhen Xi 《中国科学:化学(英文版)》2015,(3):434-435
Redox-based post-translational modification of protein thiols has become an attractive strategy in cellular homeostasis and cell signaling.Due to the reductive end of the redox buffer network,the vicinal dithiol-containing proteins(VDPs)maintains an appropriate oxidation-reduction state of proteins through the reversible transformation from vicinal dithiols to disulfide,which is responsible for a variety of 相似文献
4.
Hui Yang Mengjie Hao Yinghui Xie Xiaolu Liu Yanfang Liu Zhongshan Chen Xiangke Wang Geoffrey I. N. Waterhouse Shengqian Ma 《Angewandte Chemie (International ed. in English)》2023,62(30):e202303129
Optimizing the electronic structure of covalent organic framework (COF) photocatalysts is essential for maximizing photocatalytic activity. Herein, we report an isoreticular family of multivariate COFs containing chromenoquinoline rings in the COF structure and electron-donating or withdrawing groups in the pores. Intramolecular donor-acceptor (D-A) interactions in the COFs allowed tuning of local charge distributions and charge carrier separation under visible light irradiation, resulting in enhanced photocatalytic performance. By optimizing the optoelectronic properties of the COFs, a photocatalytic uranium extraction efficiency of 8.02 mg/g/day was achieved using a nitro-functionalized multicomponent COF in natural seawater, exceeding the performance of all COFs reported to date. Results demonstrate an effective design strategy towards high-activity COF photocatalysts with intramolecular D-A structures not easily accessible using traditional synthetic approaches. 相似文献
5.
Xiangxue Wang Shujun Yu Zhongshan Chen Wencheng Song Yuantao Chen Tasawar Hayat Ahmed Alsaedi Wei Guo Jun Hu Xiangke Wang 《中国科学:化学(英文版)》2017,60(1):107-114
To contribute to the understanding of Eu(III) interaction preperties on hydrous alumina particles in the absence and presence of fulvic acid (FA), the complexation properties of Eu(III) with hydrous alumina, FA and FA-alumina hybrids are studied by batch and time-resolved laser fluorescence spectroscopy (TRLFS) techniques. The continuous increase in the fluorescence lifetime of Eu-alumina and Eu-FA with increasing pH indicates that the complexation is accompanied by decreasing number of hydration water in the first coordination sphere of Eu(III). Eu(III) is adsorbed onto alumina particles as outer-sphere surface complexes of ≡(Al?O)?Eu· (OH)· 7H2O and ≡(Al?O)?Eu· 6H2O at low pH values, and as inner-sphere surface complexes as ≡(Al?O)2?Eu+· 4H2O at high pH. In FA solution, Eu(III) forms complexes with FA as (COO)2Eu+(H2O) x and the hydration water number in the first coordination sphere decreases with pH increasing. The formation of ≡COO?Eu?(O?Al≡)· 4H2O is observed on FA-alumina hybrids, suggesting the formation of strong inner-sphere surface complexes in the presence of FA. The surface complexes are also characterized by their emission spectra [the ratio of emission intensities of 5 D 0→7 F 1 (λ=594 nm) and 5 D 0→7 F 2 (λ=619 nm) transitions] and their fluorescence lifetime. The findings is important to understand the contribution of FA in the complexation properties of Eu(III) on FA-alumina hybrids that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Eu(III), or its analogue trivalent lanthanide and actinide ions in natural environment. 相似文献
6.
吴伟雄 《应用数学和力学(英文版)》1994,(8)
FINITEELEMENTANALYSISFORTHEUNSTEADYNEARSHORECIRCULATIONDUETOWAVE-CURRENTINTER-ACTION(I)——NUMERICALMODELWuWei-xiong(吴伟雄)(Tongj... 相似文献
7.
8.
YuchengWu YongZhang LideZhang 《中国颗粒学报》2004,2(1):19-24
Nanosized palladium particles were incorporated into mesoporous silica matrix to obtain nanocomposites using the sol-gel technique. Effects of the finely dispersed metallic palladium on the microstructure and properties of the nanocomposites were investigated. By means of X-ray diffraction and optical absorption, it was found that palladium particles were 5-9 nm in diameter and their uniform dispersion in the mesoporous silica depended on both the content of the palladium and the structural features of the silica matrix. The results showed that the mixing method of preparation led to wider size distribution of the nanosized particles as compared to the immersion method, but dispersed degree was reduced. Although the incorporation of nanosized palladium particles could not substantially induce significant structural changes of the matrix, the apparent red-shifted optical absorptions for the nanocomposites were observed as compared to the parent monolithic silica, particularly with increase in palladium loading and calcination temperature. 相似文献
9.
10.
SYNTHESIS AND CHARACTERIZATION OF SURFACE-HYPERBRANCHED MAGNETITE NANOPARTICLE FOR BOVINE SERUM ALBUMIN IMMOBILIZATION 总被引:1,自引:0,他引:1
BifengPan FengGao HongchenGu 《中国颗粒学报》2004,2(6):261-265
A hyperbranched polyamidoamine polymer was synthesized on the surface of magnetite nanoparticles to enhance bovine serum albumin (BSA) immobilization efficiency. The amount of immobilized bovine serum albumin (BSA) on the surface-hyperbranched magnetite nanoparticle was up to 2.5 times as much as that of magnetite nanoparticle modified with only amino silane. 相似文献